1. Field of the Invention
The present invention relates to a spectroscopic ellipsometer and an ellipsometry on an object.
2. Description of the Background Art
Conventionally, an ellipsometer is used as an optical measuring apparatus for measuring a thickness or an optical constant of a film formed on a semiconductor substrate (hereinafter, referred to as “substrate”) or the like. In the ellipsometer, polarized light is applied to a measurement surface of the substrate so as to incline to the measurement surface, a polarization state of reflected light reflected on the measurement surface is acquired and ellipsometry is performed to measure a film thickness or the like on the substrate. For example, Japanese Patent Application Laid-Open No. 2005-3666 (Document 1) discloses a spectroscopic ellipsometer for performing film thickness measurement and the like on a thin film formed on a substrate on the basis of a polarization state of a light at each wavelength of the reflected light.
In recent, with high definition of a pattern formed on a substrate, reduction of a film thickness on the substrate is further proceeding and it is required in the ellipsometer to achieve high precision of ellipsometry which is performed on a very fine film.
In the spectroscopic ellipsometer like in Document 1, a visible light including lights of a plurality of wavelengths is linearly polarized and applied to the substrate, and a reflected light reflected on the substrate is received to perform ellipsometry. In ellipsometry performed on a very fine film, however, measurement by entering a circularly polarized light to the substrate can increase change of outputted signal by change of film thickness, in comparison with measurement by entering linearly polarized lights to the substrate. Therefore, if ellipsometry is performed with a spectroscopic ellipsometer using the linearly polarized lights, the measurement accuracy is decreased in comparison with a laser-type ellipsometer for applying a circularly polarized laser beam (i.e., a light of one wavelength) to a substrate. At present, there is no polarizer which is capable of changing all lights of a plurality of wavelengths entering a substrate to circularly polarized lights in the spectroscopic ellipsometer.
In the spectroscopic ellipsometer, the measurement accuracy on a very fine film can be increased by using ultraviolet light as light applied to a substrate. However, in this case, since optical elements used in an optical system of the spectroscopic ellipsometer are expensive and special, the manufacturing cost of the spectroscopic ellipsometer is increased and usage environment of the spectroscopic ellipsometer is limited. In a case where a wavelength of ultraviolet light used is equal to or smaller than 200 nm, the spectroscopic ellipsometer should be used in vacuum atmosphere. Further, there is a possibility that the substrate is affected by application of the ultraviolet light.
On the other hand, in the laser-type ellipsometer, since only one wavelength of light is used for ellipsometry, measurement on a multilayer film is not suitable, and the measurement accuracy is decreased in measurement on a film with a specific thickness.